Bird Migration

Birds know when to fly south based on day length, temperature and food supply. Pre-migratory fat build-up can be extensive in some birds. Fat stores are essential because migration is a demanding activity. Some birds lose almost one percent of their body weight while migrating.

According to the University of Wisconsin, birds have been known to fly higher than Mt. Everest. Bar-headed geese have been recorded flying across the Himalayas at 29,000 feet. Other species seen above 20,000 feet include the whooper swan, the bar-tailed godwit, and the mallard duck.

(Note: birds don't fly this high just to get in the Guinness Book of Records, but rather to reach their destinations efficiently. From radar studies, scientists know that birds can change altitudes to find the best wind conditions. To fight a headwind, most birds stay low, where ridges, trees and buildings slow the wind. To ride a tailwind, they get up high where the wind is as fast as possible.)

Today's photo was taken by WPC President Larry Schweiger.

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